Innerspring assemblies for mattresses or cushions are generally composed of a plurality of spring coils arranged side-by-side in parallel rows, with parallel columns also formed orthogonal to the rows. Border wires usually encircle both the upper and lower perimeters of the support surface formed by the innerspring, such as in a mattress, and connect to terminal convolutions of the perimetrical springs by way of small diameter helical springs which wrap around the border wire.
The terminal convolutions of the coil springs are typically formed with an enlarged diameter compared to the spirals or turns, that are axially inward from the coil ends. This allows for interengagement of the spring terminal ends, as along rows and/or columns, and stabilizes the spring under compression. It is a common practice to overlap the terminal convolutions of adjacent spring coils in a row, and then wind even smaller diameter helical spring coils, referred to as cross-helicals, across the rows to encircle the overlapped terminal convolution portions.
With respect to innerspring edges, i.e., the sides of the unit, there are some general considerations of manufacture and comfort that underlie their design. In the normal use of an innerspring, the edges are subjected to greater compression forces than the interior of the innerspring, since people sit on the edge of the :innerspring when sitting or rising. The added stresses and strains on the sides can result in greater wear that is manifested in a tipping or side-sway about the border thereof. This type of wear may reduce the comfort of the item, and can result in unevenness of the side. The innerspring can further give the impression of a degree of softness it does not have, since a person sitting on the edge provides a much more concentrated load on the underlying springs than a prone individual lying upon the innerspring.
It has thus been found desirable to reinforce and provide greater stability to the edges of an innerspring assembly. For instance some, as in U.S. Pat. No. 3,262,135, have provided a resilient foam material border member perimetrically surrounding the innerspring that freely and independently supports loads apart from the innerspring. Others, as in U.S. Pat. No. 2,826,769, have devised a structure and method of adding resilient foam material about the perimetrical innerspring edge and affixed to the border strip material. Compression of this structure may create slack in the border allowing such edge arrangements to potentially disengage from respective coils, thereby reducing the effective advantages of the original structure.
Other efforts have also been directed, as shown in U.S. Pat. No. 3,618,146, to a border stabilizer formed from a plurality of foam strips positioned along the perimetrical row of spring coils of an innerspring. Each strip is slit to fit over one or more convolutions of the outermost coils. Another similar design depicted in U.S. Pat. No. 3,822,426, has a combined mattress topper pad and border stabilizer with one or more slits provided in the stabilizer portion to fit the generally rectangular cross-sectioned stabilizer onto the springs.
A method of stabilizing and reinforcing a spring border is also shown in U.S. Pat. No. 5,133,116, wherein a continuous length of resilient foam rope is wedged between convolutions of adjacent springs a plurality of turns about the perimeter of the coil spring assembly.